gallium(III) oxide

Gallium trioxide is precipitated in hydrated form upon neutralization of acidic or basic solution of gallium salt. Also, it is formed on heating gallium in air or by thermally decomposing gallium nitrate at 200–250 °C.

Crystalline Ga₂O₃ can occur in five polymorphs, α, β, γ, δ, and ε. Of these polymorphs β-Ga₂O₃ is the most thermodynamically stable phase at standard temperature and pressureBailar, J; Emeléus, H; Nyholm, R; Trotman-Dickenson, A. F. (1973). Comprehensive Inorganic Chemistry. Vol. 1, p. 1091. while α-Ga₂O₃ is the most stable polymorph under high pressures.{{Cite journal |first=Yan-Mei |last=Ma |display-authors=etal |date=2008 |title=High-Pressure and High-Temperature Behaviour of Gallium Oxide |journal=Chinese Physics Letters |volume=25 |issue=5|pages=1603–1605 |doi=10.1088/0256-307X/25/5/022 |s2cid=250882992 }}

• β-Ga₂O₃ epitaxial thin films can be deposited heteroepitaxially on substrates such as sapphire, GaN, SiC, and Si, as well as homoepitaxially. For example, ALD on sapphire substrates at temperatures between 190 °C and 550 °C have been demonstrated.{{cite journal | last1 = Rafie Borujeny | first1 = E. | last2 = Sendetskyi | first2 = O. | last3 = Fleischauer | first3 = M. D. | last4 = Cadien | first4 = K. C. | year = 2020 | title = Low Thermal Budget Heteroepitaxial Gallium Oxide Thin Films Enabled by Atomic Layer Deposition| journal = ACS Applied Materials & Interfaces | volume = 12 | issue = 39 | pages = 44225–44237 | doi = 10.1021/acsami.0c08477 | pmid = 32865966 | s2cid = 221403770 }} High-quality β-Ga₂O₃ films have also been grown using techniques such as MBE, HVPE, and MOVPE.{{Cite journal |last1=Green |first1=Andrew J. |last2=Speck |first2=James |last3=Xing |first3=Grace |last4=Moens |first4=Peter |last5=Allerstam |first5=Fredrik |last6=Gumaelius |first6=Krister |last7=Neyer |first7=Thomas |last8=Arias-Purdue |first8=Andrea |last9=Mehrotra |first9=Vivek |last10=Kuramata |first10=Akito |last11=Sasaki |first11=Kohei |last12=Watanabe |first12=Shinya |last13=Koshi |first13=Kimiyoshi |last14=Blevins |first14=John |last15=Bierwagen |first15=Oliver |date=2022-02-01 |title=β-Gallium oxide power electronics |journal=APL Materials |volume=10 |issue=2 |pages=029201 |doi=10.1063/5.0060327|bibcode=2022APLM...10b9201G |s2cid=246660179 |doi-access=free }} HVPE is preferred for vertical power semiconductor devices due to its fast growth rate.{{Cite journal |last1=Yang |first1=Duyoung |last2=Kim |first2=Byungsoo |last3=Eom |first3=Tae Hoon |last4=Park |first4=Yongjo |last5=Jang |first5=Ho Won |date=2022-03-01 |title=Epitaxial Growth of Alpha Gallium Oxide Thin Films on Sapphire Substrates for Electronic and Optoelectronic Devices: Progress and Perspective |journal=Electronic Materials Letters |volume=18 |issue=2 |pages=113–128 |doi=10.1007/s13391-021-00333-5 |bibcode=2022EML....18..113Y |s2cid=245773856 }} β-Ga₂O₃ epitaxial films grown by MOVPE exhibit higher electron mobilities and lower background carrier concentrations than those grown by other thin-film growth techniques.{{Cite journal |last1=Tsao |first1=J. Y. |last2=Chowdhury |first2=S. |last3=Hollis |first3=M. A. |last4=Jena |first4=D. |last5=Johnson |first5=N. M. |last6=Jones |first6=K. A. |last7=Kaplar |first7=R. J. |last8=Rajan |first8=S. |last9=Van de Walle |first9=C. G. |last10=Bellotti |first10=E. |last11=Chua |first11=C. L. |last12=Collazo |first12=R. |last13=Coltrin |first13=M. E. |last14=Cooper |first14=J. A. |last15=Evans |first15=K. R. |date=2018 |title=Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges |journal=Advanced Electronic Materials |volume=4 |issue=1 |pages=1600501 |doi=10.1002/aelm.201600501 |s2cid=38628999 |doi-access=free }}{{Cite journal |last1=Zhang |first1=Yuewei |last2=Alema |first2=Fikadu |last3=Mauze |first3=Akhil |last4=Koksaldi |first4=Onur S. |last5=Miller |first5=Ross |last6=Osinsky |first6=Andrei |last7=Speck |first7=James S. |date=2019-02-01 |title=MOCVD grown epitaxial β-Ga₂O₃ thin film with an electron mobility of 176 cm²/V s at room temperature |journal=APL Materials |volume=7 |issue=2 |pages=022506 |doi=10.1063/1.5058059 |bibcode=2019APLM....7b2506Z |s2cid=104453229 |doi-access=free }}

Bulk substrates of β-Ga₂O₃ can be produced, which is one of the major advantages of this material system. Bulk substrates can be produced in multiple orientations and by multiple techniques.{{Cite journal |last=Galazka |first=Zbigniew |date=2022-01-21 |title=Growth of bulk β-Ga₂O₃ single crystals by the Czochralski method |journal=Journal of Applied Physics |volume=131 |issue=3 |pages=031103 |doi=10.1063/5.0076962 |bibcode=2022JAP...131c1103G |s2cid=246074647 |doi-access=free }}{{cite web |title=Substrates |website=Novel Crystal Technology, Inc. |date=12 July 2018 |url=https://www.novelcrystal.co.jp/eng/substrates/}}File:Czorchralski Gallium.png

• α-Ga₂O₃ can be obtained by heating β-Ga₂O₃ at 65 kbar and 1100 °C. It has a corundum structure. The hydrated form can be prepared by decomposing precipitated and "aged" gallium hydroxide at 500 °C. Epitaxial thin films of α-Ga₂O₃ deposited on c-plane (0001), m-plane (10{{overline|1}}0), or a-plane (11{{overline|2}}0) sapphire substrates have been demonstrated.
• γ-Ga₂O₃ is prepared by rapidly heating the hydroxide gel at 400–500 °C. A more crystalline form of this polymorph can be prepared directly from gallium metal by a solvothermal synthesis.{{cite journal|doi=10.1002/chem.201203359|pmid=23307528|title=Structures of Uncharacterised Polymorphs of Gallium Trioxide from Total Neutron Diffraction|journal=Chemistry: A European Journal|volume=19|issue=8|pages=2803–13|year=2013|last1=Playford|first1=Helen Y.|last2=Hannon|first2=Alex C.|last3=Barney|first3=Emma R.|last4=Walton|first4=Richard I.}}
• δ-Ga₂O₃ is obtained by heating Ga(NO₃)₃ at 250 °C.{{Cite journal |last1=Li |first1=Liandi |last2=Wei |first2=Wei |last3=Behrens |first3=Malte |date=July 2012 |title=Synthesis and characterization of α-, β-, and γ-Ga₂O₃ prepared from aqueous solutions by controlled precipitation |journal=Solid State Sciences |volume=14 |issue=7 |pages=971–981 |doi=10.1016/j.solidstatesciences.2012.04.037 |bibcode=2012SSSci..14..971L }}
• ε-Ga₂O₃ is prepared by heating δ-Ga₂O₃ at 550 °C. Thin films of ε-Ga₂O₃ are deposited by means of metalorganic vapour-phase epitaxy using trimethylgallium and water on sapphire substrates at temperatures between 550 and 650 °C{{cite journal |doi=10.1016/j.jcrysgro.2016.03.013 |title=Hetero-epitaxy of ε-Ga₂O₃ layers by MOCVD and ALD |journal=Journal of Crystal Growth |volume=44 |pages=25–30 |year=2015 |last1=Boschi |first1=F. |last2=Bosi |first2=M. |last3=Berzina |first3=T. |last4=Buffagni |first4=E.|last5=Ferrari |first5=C. |last6=Fornari |first6=R.}}

Gallium(III) trioxide is amphoteric.Ebbing, Darrell D.; Gammon, Steven D. (2010) General Chemistry, 9th ed., Thomson Brooks/Cole. {{ISBN|0538497521}} It reacts with alkali metal oxides at high temperature to form, e.g., NaGaO₂, and with Mg, Zn, Co, Ni, Cu oxides to form spinels, e.g., MgGa₂O₄.Downs, Anthony John (ed.) (1993) The Chemistry of Aluminium, Gallium, Indium and Thallium. Springer. {{ISBN|075140103X}}

It dissolves in strong alkali to form a solution of the gallate ion, {{chem|Ga(OH)|4|-}}.

With HCl, it forms gallium trichloride GaCl₃.Zuckerman, J J and Hagen, A P eds. (2009) Inorganic Reactions and Methods, the Formation of Bonds to Halogens (Part 2), Wiley-VCH Verlag GmbH, {{ISBN|9780470145395}}

: Ga₂O₃ + 6 HCl → 2 GaCl₃ + 3 H₂O

It can be reduced to gallium suboxide (gallium(I) oxide) Ga₂O by H₂.{{cite journal|title=Determination of Gallium in a Cerium Surrogate and in Drops from a Copper Collector by ICP as Model Studies for the Removal of Gallium from Plutonium|author1= Koch, H. F. |author2=Girard, L. A. |author3=Roundhill, D. M. |journal= Atomic Spectroscopy|year= 1999|volume= 20|issue= 1|page= 30}} or by reaction with gallium metal:Greenwood, N.N.; Emeleus, H. J. and Sharpe, A. G. (1963) "The chemistry of Gallium" in Advances in Inorganic Chemistry and Radiochemistry, Vol. 5, Elsevier, Academic Press

: Ga₂O₃ + 2 H₂ → Ga₂O + 2 H₂O

: Ga₂O₃ + 4 Ga → 3 Ga₂O

β-Ga₂O₃, with a melting point of 1900 °C, is the most stable crystalline modification. The oxide ions are in a distorted cubic closest packing arrangement, and the gallium (III) ions occupy distorted tetrahedral and octahedral sites, with Ga–O bond distances of 1.83 and 2.00 Å respectively.King, R. B. (1994) Encyclopedia of Inorganic Chemistry. Vol. 3. p. 1256. {{ISBN|978-0-470-86078-6}}.

α-Ga₂O₃ has the same structure (corundum) as α-Al₂O₃, wherein Ga ions are 6-coordinate.{{cite journal |doi=10.1111/j.1151-2916.1973.tb12471.x |title=Thermal Expansion of Alpha Ga₂O₃ |journal=Journal of the American Ceramic Society |volume=56 |issue=4 |pages=229 |year=1973 |last1=Eckert |first1=L. J. |last2=Bradt |first2=R. C. |author-link2=Richard C. Bradt}}{{cite journal |last1=Marezio |first1=M. |last2=Remeika |first2=J. P. |title=Bond Lengths in the α-Ga₂O₃ Structure and the High-Pressure Phase of Ga_2−xFe_xO₃ |journal=The Journal of Chemical Physics |date=1 March 1967 |volume=46 |issue=5 |pages=1862–1865 |doi=10.1063/1.1840945 }}

γ-Ga₂O₃ has a defect spinel structure similar to that of γ-Al₂O₃.{{Greenwood&Earnshaw|page=247}}

ε-Ga₂O₃ films deposited by metalorganic vapour-phase epitaxy show a columnar structure with orthorhombic crystal symmetry. Macroscopically, this structure is seen by X-ray crystallography as hexagonal close packed.{{cite journal|doi=10.1039/C7CE00123A|title=The real structure of ε-Ga₂O₃ and its relation to κ-phase|journal=CrystEngComm|volume=19|issue=11|pages=1509–1516|year=2017|last1=Cora|first1=I|doi-access=free|hdl=10831/67366|hdl-access=free}}

κ-Ga₂O₃ has an orthorhombic structure and forms with 120° twin domains, resulting in hexagonal symmetry which is often identified as ε-Ga₂O₃.{{Cite journal |last1=Fornari |first1=R. |last2=Pavesi |first2=M. |last3=Montedoro |first3=V. |last4=Klimm |first4=D. |last5=Mezzadri |first5=F. |last6=Cora |first6=I. |last7=Pécz |first7=B. |last8=Boschi |first8=F. |last9=Parisini |first9=A. |last10=Baraldi |first10=A. |last11=Ferrari |first11=C. |last12=Gombia |first12=E. |last13=Bosi |first13=M. |date=2017-11-01 |title=Thermal stability of ε-Ga₂O₃ polymorph |journal=Acta Materialia |volume=140 |pages=411–416 |doi=10.1016/j.actamat.2017.08.062 |bibcode=2017AcMat.140..411F }}

{{empty section|date=February 2025}}

Gallium(III) oxide has been studied for usage as passive components in lasers,{{Cite journal |last1=Deng |first1=Huiyang |last2=Leedle |first2=Kenneth J. |last3=Miao |first3=Yu |last4=Black |first4=Dylan S. |last5=Urbanek |first5=Karel E. |last6=McNeur |first6=Joshua |last7=Kozák |first7=Martin |last8=Ceballos |first8=Andrew |last9=Hommelhoff |first9=Peter |last10=Solgaard |first10=Olav |last11=Byer |first11=Robert L. |last12=Harris |first12=James S. |date=April 2020 |title=Ga₂O₃-Based Optical Applications: Gallium Oxide for High-Power Optical Applications (Advanced Optical Materials 7/2020) |journal=Advanced Optical Materials |volume=8 |issue=7 |pages=2070026 |doi=10.1002/adom.202070026 |s2cid=216243413 |doi-access=free }} phosphors, and luminescent materials{{Cite journal |last1=Nogales |first1=E |last2=Méndez |first2=B |last3=Piqueras |first3=J |last4=García |first4=J A |date=2009-03-18 |title=Europium doped gallium oxide nanostructures for room temperature luminescent photonic devices|journal=Nanotechnology |volume=20 |issue=11 |pages=115201 |doi=10.1088/0957-4484/20/11/115201 |pmid=19420434 |bibcode=2009Nanot..20k5201N |s2cid=23058882 |url=https://eprints.ucm.es/id/eprint/24274/1/MendezBianchi15.pdf }} as well as active components for gas sensors, power diodes,{{Cite journal |last1=Li |first1=Wenshen |last2=Nomoto |first2=Kazuki |last3=Hu |first3=Zongyang |last4=Jena |first4=Debdeep |last5=Xing |first5=Huili Grace |date=January 2020 |title=Field-Plated Ga₂O₃ Trench Schottky Barrier Diodes With a BV²/R_on,sp of up to 0.95 GW/cm² |journal=IEEE Electron Device Letters |volume=41 |issue=1 |pages=107–110 |doi=10.1109/LED.2019.2953559 |s2cid=209696027 |doi-access=free }} and power transistors.{{Cite journal |last1=Xia |first1=Zhanbo |last2=Xue |first2=Hao |last3=Joishi |first3=Chandan |last4=Mcglone |first4=Joe |last5=Kalarickal |first5=Nidhin Kurian |last6=Sohel |first6=Shahadat H. |last7=Brenner |first7=Mark |last8=Arehart |first8=Aaron |last9=Ringel |first9=Steven |last10=Lodha |first10=Saurabh |last11=Lu |first11=Wu |last12=Rajan |first12=Siddharth |date=July 2019 |title=β-Ga₂O₃ Delta-Doped Field-Effect Transistors With Current Gain Cutoff Frequency of 27 GHz |journal=IEEE Electron Device Letters |volume=40 |issue=7 |pages=1052–1055 |doi=10.1109/LED.2019.2920366 |bibcode=2019IEDL...40.1052X |s2cid=195439906 |doi-access=free }} Since the first publication in January 2012 by the National Institute of Information and Communications Technology, in collaboration with Tamura Co., Ltd. and Koha Co., Ltd. of the world's first single-crystal gallium oxide (Ga₂O₃) field-effect transistors, the predominant interest in gallium oxide is in the β-polymorph for power electronics.{{Cite journal |last1=Higashiwaki |first1=Masataka |last2=Sasaki |first2=Kohei |last3=Kuramata |first3=Akito |last4=Masui |first4=Takekazu |last5=Yamakoshi |first5=Shigenobu |date=2012-01-02 |title=Gallium oxide (Ga₂O₃) metal-semiconductor field-effect transistors on single-crystal β-Ga₂O₃ (010) substrates |journal=Applied Physics Letters |volume=100 |issue=1 |pages=013504 |doi=10.1063/1.3674287 |bibcode=2012ApPhL.100a3504H }}

Monoclinic β-Ga₂O₃ has shown increasing performance since 2012 approaching state of the art GaN and SiC power devices. β-Ga₂O₃ Schottky diodes have exceeded breakdown voltages of 2400 V. β-Ga₂O₃/NiO_x p–n diodes have exhibited breakdown voltages over 1200 V.{{Cite journal |last1=Wang |first1=Chenlu |last2=Gong |first2=Hehe |last3=Lei |first3=Weina |last4=Cai |first4=Yuncong |last5=Hu |first5=Zhuangzhuang |last6=Xu |first6=Shengrui |last7=Liu |first7=Zhihong |last8=Feng |first8=Qian |last9=Zhou |first9=Hong |last10=Ye |first10=Jiandong |last11=Zhang |first11=Jincheng |last12=Zhang |first12=Rong |last13=Hao |first13=Yue |date=April 2021 |title=Demonstration of the p-NiOx/n-Ga₂O₃ Heterojunction Gate FETs and Diodes With BV2/Ron,sp Figures of Merit of 0.39 GW/cm² and 1.38 GW/cm² |journal=IEEE Electron Device Letters |volume=42 |issue=4 |pages=485–488 |doi=10.1109/LED.2021.3062851 |bibcode=2021IEDL...42..485W |s2cid=232372680 }} β-Ga₂O₃ MOSFETs have individually achieved figures of merits of  f_T of 27 GHz, f_MAX of 48 GHz,{{Cite arXiv |last1=Saha |first1=Chinmoy Nath |last2=Vaidya |first2=Abhishek |last3=Bhuiyan |first3=A. F. M. Anhar Uddin |last4=Meng |first4=Lingyu |last5=Zhao |first5=Hongping |last6=Singisetti |first6=Uttam |date=2022-11-02 |title=Beta-Ga₂O₃ MOSFETs with near 50 GHz fMAX and 5.4 MV/cm average breakdown field |class=cond-mat.mtrl-sci |eprint=2211.01088 }} and 5.4 MV/cm average breakdown field. This field exceeds that which is possible in SiC or GaN.

ε-Ga₂O₃ thin films deposited on sapphire show potential applications as solar-blind UV photodetector.

{{Reflist|30em}}

{{Gallium compounds}}

{{Oxides}}

{{oxygen compounds}}

{{Use dmy dates|date=March 2018}}

{{DEFAULTSORT:Gallium(Iii) Oxide}}

Category:Gallium compounds

Category:Sesquioxides